There has been progress in development of electrical energy storage devices configured to interrupt current flowing between electrode terminals (positive terminal and negative terminal) in case where an electrical energy storage device is overcharged or short-circuiting occurs therein. The current interruption device is disposed between the electrode terminal and a corresponding electrode (between a positive terminal and a positive electrode, or between a negative terminal and a negative electrode). International Publication No. WO 2013/154166 A1 discloses a current interruption device including a first conductive member fixed to a casing, and a second conductive member disposed at a position opposed to the first conductive member. Hereinafter, International Publication No. WO 2013/154166 A1 is referred to as Patent Literature 1. The first conductive member is connected to an electrode terminal, and the second conductive member is connected to an electrode. A first deformable member is disposed between the first conductive member and the second conductive member. A center portion of the first deformable member is configured to be in contact with the second conductive member when pressure in the casing is equal to or less than a predetermined value, and configured to be brought out of contact with the second conductive member when the pressure in the casing exceeds the predetermined value. In Patent Literature 1, further, a second deformable member is disposed on a side opposite to the first deformable member relative to the second conductive member. The second deformable member is provided with a projection. When the pressure in the casing exceeds the predetermined value, the second deformable member is configured to be deformed and the projection is brought into contact with the second conductive member to break the second conductive member. By fracturing the second conductive member, the first deformable member and the second conductive member are brought out of contact with each other. With this, a conduction between the electrode terminal and the electrodes is interrupted.